Tina curled an 8 inch by 10 inch rectangular piece of paper along one of its sides to form an open cylinder with a height of 10 inches. Which measure of the cylinder will be 8 inches?
the radius of the base
the diameter of the base
the area of the base
the circumference of the base

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?